The Oregon Treaty set much of the U.S.-British North America border at the 49th parallel.
Signed on June 15, 1846, the Oregon Treaty ended the long-running Oregon boundary dispute between the United States and the United Kingdom. It divided the jointly occupied Oregon Country along the 49th parallel of north latitude, extending the mainland boundary westward from the Rocky Mountains toward the Pacific.
The settlement followed the earlier Convention of 1818, which had already established the 49th parallel east of the Rockies while leaving the Oregon Country under joint occupation. American expansionists had demanded territory as far north as 54°40′, producing the slogan “Fifty-Four Forty or Fight,” but diplomats ultimately accepted a compromise.
The treaty was not a perfectly straight-line settlement. Vancouver Island remained British, and the marine boundary through the Strait of Georgia and Strait of Juan de Fuca was disputed. That uncertainty helped cause the bloodless Pig War over the San Juan Islands in 1859; arbitration finally awarded the islands to the United States in 1872. The 49th parallel later became the principal Canada–United States land border in the region.